Add the necessary value to each side of the equation to isolate the #x# terms on one side of the equation and the constants on the other side of the equation while keeping the equation balanced:
#-30x - 6 + color(red)(30x) + color(blue)(3) = -9x - 3 + color(red)(30x) + color(blue)(3)#
#-30x + color(red)(30x) - 6 + color(blue)(3) = -9x + color(red)(30x) - 3 + color(blue)(3)#
#0 -6 + color(blue)(3) = -9x + color(red)(30x) - 0#
#-6 + color(blue)(3) = -9x + color(red)(30x)#
We can next combine like terms:
#-3 = (-9 + 30)x#
#-3 = 21x#
Now, we can solve for #x# while keeping the equation balanced:
#-3/color(red)(21) = (21x)/color(red)(21)#
#-1/7 = (color(red)(cancel(color(black)(21)))x)/cancel(color(red)(21))#
#-1/7 = x#
#x = -1/7#
